Cornwall IV and subwoofers

For me, and again for me... I have Heresy IV's with an SVS PB2000 pro. It's everything I need. The Heresy's with my Mac 240 are a sweet combination. The SVS gives every recording an easy weight and presence. I really like the SVS mobile app and pre-sets, really lets me dial everything in. Just my two bits..

I have the Cornwall 4’s in a 14x30 room with an SVS SB3000 sub. The sub fills in the bottom octave nicely. I never thought a sub was necessary until I actually tried it. Big improvement. 

Piggy-backing on what @jbhiller said very well, I use the Cornwall IVs with a pair of REL t7i's, speaker level from a Pass INT-60. The RELs have 8" active, 10" down-firing passive. They're small enough that the OP might be able to accommodate a pair. I've tried to cross them around 30-35, although REL doesn't make it easy to be precise in that regard. As jb said, they're not really necessary, but I like to think they add just a touch to the Cornwalls' palpable sense of presence.

I have a pair of Klipsch corner horns, just the bass section.  The go to about 40 Hz and at 106 dB/1w are effective for most listening.  I would not add a sub, but built one anyway. 

I call the Klipsch "subs" because that seems to be the vernacular. 

I do have a sub-sub, which is a 14' transmission line with 4 15s.  Three of those.  TLs are narrow band but efficient.  I can't measure the SPL but it should be flat to 4 Hz and judging from vertical floor movement, about 5.2 Richter.  Good for rocket launches, end of world movies and such.  Maybe some music. 

Plenty of good stuff to digest here. Thanks again to all respondents.

Bill